Chitosan/calcium phosphates nanosheet as a vaccine carrier for effective cross-presentation of exogenous antigens

Chitosan/calcium phosphate nanosheet as a promising antigen carrier was prepared via the direct mixture of modified chitosan, PBS and CaCl₂. Specifically, chitosan was modified with catechol groups, and its water solubility under neutral conditions was improved. Then, nanosheet was formed by mixing modified chitosan and PBS followed by addition of CaCl₂. Antigen was entrapped into the nanosheet via coprecipitation during its preparation. The nanosheet composed of CaHPO₄·2H₂O crystals, was internalized by dendritic cells (DCs) via macropinocytosis with enhanced efficiency. The antigen endosomal escape induce by nanosheet was successful observed with intracellular Lysotracker and Lamp-1 staining. Moreover, DCs activation was triggered by the nanosheet along with the up-regulated expression of co-stimulation marker and production of Th1-type cytokines. More importantly, cross-presentation of antigens achieved by the nanosheet was markedly increased when compared to free antigen. Therefore, chitosan/calcium phosphate nanosheet could be used as a vaccine carrier for effective cross-presentation of exogenous antigens.